The present invention relates to a method of detecting abnormalities of cells having decreased level of Glycine N-methyltransferase (GNMT) and to a method of correcting the abnormalities of cells.
One of the most common types of human diseases throughout the world due to cell abnormalities is cancer, which is also the leading cause of death nowadays. Cancers are fully developed (malignant) tumors with a specific capacity to invade and destroy the underlying mesenchyme, i.e., local invasion. In some cases, invading tumor cells may further penetrate lymphatic vessels or blood vessels newly formed in the tumor and then may be carried to local lymph nodes or even to distant organs where they may produce secondary tumors (metastases). Tumors are usually recognized by the fact that the cells, which may arise from any tissue, are no longer responsive to at least some normal growth controlling mechanisms and hence show abnormal growth. Apart from the cancer, a tumor may merely develop locally and never become malignant, i.e., a benign tumor. Alternatively, cells of a tumor may merely have morphological appearances of cancer cells but remain in their place, i.e., an in situ tumor, although in this case the tumor may sometimes precede a cancer in situ.
There are no absolute methods for diagnosing or assessing the degree of malignancy of tumors. However, among the methods, microscopic examination of tissue is still the most reliable method for routine use. In a pathologic study, tumors can be graded by making an approximate assessment of the degree of structural dedifferentiation (anaplasia) based on histological and cytological criteria by microscopically examining sections thereof. However, on one hand, some cells may have lost their specific structural characters but still retain differentiated biochemical features, while others may still appear differentiated in structure but have lost many normal function attributes. On the other hand, a tumor is not homogeneous and may contain areas with more than one tumor grade, therefore, a developed tumor may consist of a mixed population of cells which may differ in structure, function, growth potential, resistance to drugs or X-rays and ability to invade and metastasize. The two limitations reduce the effectiveness of histological examination of tumors. In another aspect, such an examination by sampling specimens is not suitable for investigations on a large scale.
Many attempts to find absolute markers of malignancy have long been made. Other attempts to identify tumor-specific or tumor-associated proteins, either by direct measurement or by developing specific antibodies to these proteins, are still being made at the moment. They seem to be promising approaches not only in diagnosis but also in providing strategies of destroying cancer cells. A variety of substances wherein the presence or concentrations thereof in vivo may be indicative for certain cancers have been reported, such as oncofetal antigens, e.g., alpha-fetoprotein; serum proteins, e.g., ferritin; enzymes; polyamines; ectopic hormones; cell markers; receptors or tumor-associated viral antigens. However, the most commonly used method of diagnosis of cancers depends on histology rather than any of the above substances. The lack of any absolute markers is a major deficiency in studying cancer.
Recent observations provide some contemplations in searching for the substances intimately associated with carcinogenesis. Cancer is appreciated as a result of multiple gene aberrations which cause both the activation of oncogenes and inactivation of tumor suppressor genes. Further, the differential expression of those critical genes associated with oncogenesis is able to be reflected at the messenger RNA (mRNA) level in cells. For effectively screening the altered ones of interest amongst a great amount of mRNA, a powerful tool, i.e., differential display, has been established to identify and isolate a small subset of genes which are differentially expressed between tumorous and normal cells (Liang et al., Cancer Research 52, 6966-6968, 1992).
It is surprisingly found in the present invention that the GNMT gene is differentially expressed between normal and tumorous cells with a significant distinction. An objective of the present invention is to provide a method of detecting abnormalities of cells by determining the relative levels of gene expression of GNMT. Furthermore, another objective of the present invention is to provide a method of correcting the abnormalities of cells by delivering GNMT into the abnormal cells.